Solids mixing in a down-flow circulating fluidized bed of 0.418-m in diameter

The axial and lateral solids mixing in a down-flow circulating fluidized bed of 0.418-m diameter was investigated by a pneumatic injection phosphor tracer technique (PIPTT). The axial and lateral solids dispersion were determined by measuring the solids RTD at same axial but different lateral positions using point sources for tracer injection. A two-dimensional dispersion model described the measured RTD curves satisfactorily. The results were compared to those obtained in the small scale downers and the scale-up effect was investigated. The axial solids Peclet number Pea is around 110 and invariable with changing Ug, Gs and ɛs, while the lateral solids Peclet number Per is linearly increasing with ɛs. And Per is found to decrease with the square root of inner diameter (ID) in comparison with the results obtained in small ID downers. Correlation of Per, Per = (15 + 70.7 ɛs)D− 0.5, is proposed.